Sort systems in stdout

The script displays 'Impacted packages' for each system.
This ensures that the systems are enumerated in the canonical order.

Author: GaetanLepage

nixpkgs_review/report.py

@@ -6,7 +6,7 @@
 from typing import Literal
 
 from .nix import Attr
-from .utils import System, info, link, skipped, warn
+from .utils import System, info, link, skipped, system_order_key, warn
 
 
 def print_number(
@@ -141,7 +141,7 @@ def order_reports(reports: dict[System, SystemReport]) -> dict[System, SystemRep
     return dict(
         sorted(
             reports.items(),
-            key=lambda item: "".join(reversed(item[0].split("-"))),
+            key=lambda item: system_order_key(system=item[0]),
             reverse=True,
         )
     )

nixpkgs_review/review.py

@@ -16,7 +16,7 @@
 from .github import GithubClient
 from .nix import Attr, nix_build, nix_eval, nix_shell
 from .report import Report
-from .utils import System, current_system, info, sh, warn
+from .utils import System, current_system, info, sh, system_order_key, warn
 
 # keep up to date with `supportedPlatforms`
 # https://github.com/NixOS/ofborg/blob/cf2c6712bd7342406e799110e7cd465aa250cdca/ofborg/src/outpaths.nix#L12
@@ -212,8 +212,14 @@ def build_commit(
             for system in self.systems
         }
 
-        changed_attrs = {}
-        for system in self.systems:
+        # Systems ordered correctly (x86_64-linux, aarch64-linux, x86_64-darwin, aarch64-darwin)
+        sorted_systems: list[System] = sorted(
+            list(self.systems),
+            key=system_order_key,
+            reverse=True,
+        )
+        changed_attrs: dict[System, set[str]] = {}
+        for system in sorted_systems:
             changed_pkgs, removed_pkgs = differences(
                 base_packages[system], merged_packages[system]
             )

nixpkgs_review/utils.py

@@ -76,3 +76,20 @@ def nix_nom_tool() -> str:
         return "nom"
 
     return "nix"
+
+
+def system_order_key(system: System) -> str:
+    """
+    For a consistent UI, we keep the platforms sorted as such:
+    - x86_64-linux
+    - aarch64-linux
+    - x86_64-darwin
+    - aarch64-darwin
+
+    This helper turns a system name to an alias which can then be sorted in the anti-alphabetical order.
+    (i.e. should be used in `sort` with `reverse=True`)
+
+    Example:
+    `aarch64-linux` -> `linuxaarch64`
+    """
+    return "".join(reversed(system.split("-")))